The invention relates to an electrodeless low-pressure discharge lamp having a lamp vessel which is sealed in a gas-tight manner and is filled with a metal vapor and a rare gas. The lamp vessel comprises a glass envelope which is connected in a gas-tight manner to the edge of a conically widening collar at the end of a tubular part of a sealing member also made of glass. The tubular part accommodates a rod-shaped core of a magnetic material by means of which a discharge is generated in the lamp vessel during operation of the lamp. The known lamp has an exhaust tube which extends parallel to the longitudinal axis of the tubular part of the sealing member and terminates at the wall of the conical collar. A lamp of this type is known from "Neues aus der Technik", 1986, 1.
The sealing member in the known lamp is in the form of a stem which is connected in a gas-tight manner by means of sealing glass to the envelope-shaped part of the lamp vessel. The use of a stem in itself is quite conventional in tubular low-pressure mercury discharge lamps provided with electrodes and in incandescent lamps. In these lamps the stems are provided with electrodes and a tubular exhaust tube which terminates in a so-called pinch which is located on or near the longitudinal axis of the stem. An exhaust tube is required for exhausting the lamp vessel, that is to say, filling the lamp vessel with a desired rare gas atmosphere, degassing of electrodes, the wall and other components of the lamp vessel, etc.
However, due to the presence of the rod-shaped magnetic core there is no space for an exhaust tube in the centrally located tubular part of the sealing member formed as a stem in an electrodeless lamp. However, these lamps also require exhausting of the lamp vessel.
In the known lamp the exhaust tube is therefore connected to the conical collar of the sealing member. For the purpose of satisfactory progress of exhausting in a bulk manufacturing process it is desirable that an exhaust tube extends in the direction of the longitudinal axis of the lamp vessel (the same direction as the longitudinal axis of the tubular part). When the end of an exhaust tube engages a wall which extends obliquely with respect to the said longitudinal axis, it is necessary that prior to or subsequent to fixation to the said wall part the exhaust tube is bent until the correct position (in the direction of the longitudinal axis) for exhausting is reached. This bending process is an additional time-consuming step in the manufacturing process creating a ready risk of breakage of the sealing member or the exhaust tube.